题目内容：

look who ______(cut) trees over there?--they ______ down a lot of trees last sunday.

优质解答

are cutting , cut
根据look 判断,第一空用现进,再根据第二句中的they,可知第一空填are cutting 而不是is cutting . 根据过去时间 last sunday判断第二空用过去式cut . this was his first visit ___ china ,he said the trip ____china was very interesting.
A.to,to B. to ,for选A

追问：

who 是代词。应用三单？

追答：

在不知道多少人的情况下,用三单,如: Who is knocking at the door ? 但此句后面有个they,因此要用are cutting .